1. Field of the Invention
The present invention relates to a conveying device and a conveying control method and particularly to a conveying device and a conveying control method in which a phase of a conveying roller and a position of a print medium are controlled.
2. Description of the Related Art
Conventionally, in an inkjet printer, a high-accuracy roller in which a metal shaft is coated with a grinding stone has been used as a main conveying roller. As a sub conveying roller also functioning as a discharge roller located on the downstream of the main conveying roller, a rubber roller having an accuracy lower than the main conveying roller and formed by rubber being attached to a metal shaft has been used.
According to this configuration, a conveying error is large in delivery of a print medium from the main conveying roller to the sub conveying roller and in conveyance only with the sub conveying roller, and it has been difficult to realize higher image quality and higher throughput.
As a measure against that, printing of a test pattern on a print medium and reading and analysis of the printed data by a scanner have been performed in recent years. A technology is proposed that characteristics (outer diameter, deflection, and the like) of the main and sub conveying rollers are obtained by performing the above-described analysis using a test pattern, and the obtained result is fed back as a correction value in printing and conveyance is performed (Japanese Patent Laid-Open No. 2005-007817). When this type of method is used, a technology of controlling a phase of the main conveying roller or the sub conveying roller and a position of the print medium becomes important for the following two reasons.
When the test pattern is printed, the sub conveying roller cannot print one cycle since a length of a single print medium is not sufficient. Thus, it is necessary to separate a print for one cycle into two sheets for printing. Thus, the first reason is that if the print for one cycle is separated into two sheets for printing, the phase of the sub conveying roller and the position of the print medium should be controlled so that there is no conveying error.
Moreover, a second reason is that the phases of the main conveying roller and the sub conveying roller should be fixed to optimal phases when the print medium is delivered from the main conveying roller to the sub conveying roller so that the conveying error is stabilized and can be easily corrected. This technology is proposed in Japanese Patent Laid-Open No. 2010-046994, for example.
According to the configuration described in Japanese Patent Laid-Open No. 2010-046994, the conveying roller and a feeding roller need to be driven and controlled, respectively in order to match the phase of the conveying roller with the position of the print medium. This can be realized by driving the conveying roller and the feeding roller by separate motors and by controlling the rollers individually, for example. Alternatively, this can be realized by coupling the conveying roller and the feeding roller with a motor through drive switching device, respectively, by switching driving of the motor by the drive switching device and by controlling rotation of the conveying roller or the feeding roller.
However, such realizing device has many demerits such as cost increase caused by provision of a plurality of motors, reduction in a throughput due to operation of the drive switching device, complication of drive transmitting device and control and the like.